Recently, it has been suggested to employ holographic data storage and retrieval systems for replacement of or complementary to existing systems employing magnetic tape or discs, punched cards or tape, etc. In particular, it has been suggested to holographically record information on photographic plates which are addressed by deflecting a light beam to a particular space on the plate with another hologram or by moving the plate on an X-Y table to align it with the light beam.
Such systems, though workable, have drawbacks. A large volume of data to be stored requires large photographic plates which can be too bulky for some applications. In addition, where holographic beam deflection is employed, a substantial portion of the overall photographic plate area might be unused if, for one reason or another, no information is to be recorded at a particular address. Lastly, the X-Y positioning of photographic plates is relatively expensive due to the intricate mechanism necessary to effect planar movements of the plate. Thus, though proposed in the past, such prior art systems have never matured into a commercially feasible product.
Even with the proliferation of data storage and retrieval systems experienced during the last several years, no significant progress has been made in instances where the same data must be retrieved at many different, widely spaced apart locations. This is most commonly encountered in commercial credit verification systems, for credit checks of customers in a department store, a chain store, the retail outlets of a major oil company or at places where one of the national or worldwide credit card systems is accepted. In all instances there are hundreds of thousands to millions of credit holders, only a small proportion of which represent bad credit risks. In the past the credit issuing store, firm or organization (hereinafter "creditor") periodically provided a list of invalid or stolen credit cards which were used at the point of sale for checking customers' credit. In large credit card systems such lists are frequently not used by sales personnel because it is too time consuming to search the list each time a sale is made.
Attempts have also been made to increase the efficiency of verifying credit standing with on-line computer systems in which a central computer could be addressed by the sales personnel by telephone or otherwise. Such systems provide access to constantly updated credit information. However, even these credit checks are time consuming, frequently involve costly long-distance calls that are sometimes hard to complete and require high-priced computers. Thus, such systems are too expensive to warrant widespread use and they have not become generally accepted.
More recently it has been suggested to employ holographic data storage and retrieval systems as particularly well suited for credit verification systems. In such systems an independent holographic data storage and retrieval unit is placed at the point of sale for checking the credit of all customer's to whom credit is to be extended to determine whether a particular customer's credit was revoked or if the customer attempts to perpetrate fraud by claiming the credit of another as is commonly done by using stolen credit cards. Such holographic systems were to employ the already described holographic memories. The holographic memories are ideally suited for this purpose because they are inexpensive to update and to distribute by mail. Moreover, the memories are permanent and indelible.
Nevertheless, the practical implementation of the holographic systems was not up to par with their conceptual usefulness. Consequently, the suggestions remained just that and never materialized into a useful form. Thus, large verification systems such as credit checks continue to employ cumbersome, out-dated and largely ineffective methods.